10-08-2012, 02:00 PM
BASIC OF APPLIED MECHANICAL MEASUREMENT
metrology notes.pdf (Size: 2.24 MB / Downloads: 490)
Introduction
Basic quantities for measurement in mechanical field are measurement for length, mass, time, temperature and angle. These quantities can be obtained using certain measurement devices. Several measurement devices can measure some of the quantities, while the remains need to use specific measurement devices.
Classification of mechanical measurement and its measurement devices that will be discussed are as follows:
Linear Dimension Measurement
Micrometer
A micrometer is a widely used device in mechanical engineering for precisely measuring thickness of blocks, outer and inner diameters of shafts and depths of slots. Appearing frequently in metrology, the study of measurement, micrometers have several advantages over other types of measuring instruments like the Vernier caliper - they are easy to use and their readouts are consistent. There are three types of micrometers based on their application:
• External micrometer
• Internal micrometer
• Depth micrometer
Construction
The indicating scale is constructed so that when its zero point is coincident with the start of the data scale, its gradations are at a slightly smaller spacing than those on the data scale and so do not coincide with any on the data scale. N gradations of the indicating scale would cover N-1 gradations of the data scale (where N is the number of divisions the maker wishes to show at the finer level).
Tape measure
A tape measure or measuring tape is a ribbon of cloth, plastic, or metal with linear-measure markings, often in both imperial and metric units. Surveyors use tape measures in lengths on the order of hectometres. It is a convenient measuring tool. Its flexibility allows for a measure of great length to be easily carried in pocket or toolkit and permits one to measure around curves or corners.
Tape measures intended for use in tailoring or dressmaking are typically made of flexible cloth or plastic, while those designed for carpentry or construction often use a stiff, curved metallic ribbon that can remain stiff and straight when extended, but retracts into a coil for convenient storage. This type of tape measure will have a floating tang on the end to aid measuring. The tang will float a distance equal to its thickness, to allow accurate measurement whether the tape is in tension or compression. A tape measure of 25 or even 100 feet can wind into a relatively small container.